1. Field of the Invention
This invention relates to an automated process for the manufacture of lead-acid batteries and an associated apparatus and new features of battery design and construction resulting therefrom. More specifically, this invention pertains to an improved lead-acid battery and an efficient method and associated apparatus for its manufacture in a large variety of shapes and sizes for uses such as automotive starting, traction, industrial, and small sealed lead-acid battery applications.
2. Description of the Prior Art
Lead acid batteries are a well known source of energy. The conventional lead-acid battery consists of a plurality of positive plates and a plurality of negative plates separated by porous separators. The plates are made by pasting a leady oxide material over the lead wire grid. Separate positive and negative plates are pasted and cured, with each of the plates having a lug disposed on the top portion of the plate. Prior to being placed in the battery container, a separator is placed between each plate and the negative and positive plate lugs are joined by two separate plate straps, one for the positive plate lugs and one for the negative plate lugs. Once placed into the container the intercell connections are made and the battery container and cover are sealed together. The positive and negative posts are welded in the cover, the acid is added, and the battery is formed electrochemically.
As is well known, the chemical reaction between the battery plates and the acid produces an electric charge which can be used to start an automobile, for example. The chemical reaction is reversible so that a generator in an automobile, for example, can recharge the battery.
There are many known processes for making lead-acid batteries. One known process is disclosed in U.S. Pat. No. 4,271,586. This process involves feeding a ribbon of lead into an inline expander (such as is described in U.S. Pat. No. 3,853,626) to produce a continuous bilateral length of grid making stock. The stock has a central unexpanded strip and two unexpanded strips at the lateral edges thereof. Between the central unexpanded strip and each lateral edge, there is a network of grid wires formed by the expander. The grid-making stock enters a belt paster for filling the grid network with battery paste. The pasting machine sandwiches the grid making stock and paste between paper strips fed from paper rolls. Plate forming stock exits the paster and passes into an oven for flash drying. Following flash drying and cutting, the plate forming stock is ready for curing. After curing, a stacker accumulates the plates for subsequent processing into a lead-acid battery.
The subsequent processing involves making a battery element out of the negative and positive battery plates and the separators. After this, the positive lugs of the battery elements and the negative lugs of the battery elements are separately joined by exposing each of them to molten lead, which subsequently hardens to form the plate strap. The elements are then placed into the container, the intercell connection made, and the battery container and cover are sealingly joined. Finally, the posts are formed on the battery cover.
It will be appreciated that the battery manufacturing process broadly involves five related aspects. The first aspect is the manufacturing of the battery grid. The second aspect is the pasting of the grid. Curing of the battery plates is the third aspect. The fourth aspect involves cutting and stacking of the battery plates and the separator to form a battery element. The fifth aspect is the containerization of one or a plurality of the battery elements to form the final battery product.
Existing manufacturing processes and the battery designs that result therefrom have several disadvantages. Each of the five aspects mentioned hereinbefore will be discussed with reference to the disadvantages related to not only the known processes involved with the five aspects but also the inadequacies of the product produced by the known processes.
Starting with the first aspect, the battery grid, it is known to mold cast or continuously cast the grids having pre-positioned lugs. It has also been known that grids may be formed by expanding a lead strip to form the reticulated grid wire portion and the grid border portions. See U.S. Pat. Nos. 3,853,626; 4,247,970; and 4,271,586.
In these processes, the grid border and the grid wires have a uniform thickness. The use of permanent molds in the casting of the grid and the pre-positioning of the lug in continuous casting limit the use of a particular grid pattern to a single battery. This results in the need for a large number of molds and associated tooling to produce the wide variety of batteries required in the marketplace. Further, as the grid requires greater electrical conductivity towards the top border containing the lug, the use of a uniform cross-section equivalent to the maximum section needed to conduct the electricity generated in the plate results in an inefficient use of lead and needlessly increases the weight and cost of the battery. Another problem encountered in the use of conventional grids of uniform cross-section is the tendency for plates to separate from cast-on plate straps in the containerization process if a metallurgical bond is not achieved during the cast-on operation.
In the second aspect, the battery plates are normally produced by passing cast grids through an orifice-type or belt-type paster. See, e.g., U.S. Pat. Nos. 3,758,340; 3,894,886; 3,951,688; and 4,318,430. Plates may be "flush pasted" (i.e., the thickness of the paste layer is approximately equal to thickness of the grid) or "overpasted" on one side (i.e., the paste layer is flush with one surface of the grid but extends beyond the surface of the grid on the opposite side). In either case, the surfaces of the paste on opposite sides of the plate are normally smooth and parallel.
Several problems are associated with the herein-before described method and battery plate produced. First, "flush pasting" usually leaves lead grid wires exposed to acid during operation of the battery, thereby increasing the chance of grid corrosion which, in turn, shortens battery life. Second, plates must normally be flat to permit proper stacking during transport and curing. Third, both belt pasters and orifice pasters have difficulty in "overpasting" the grid on both sides. That is, "overpasting" the underside of the grid is extremely difficult so that "overpasted" plates are usually produced with only the upper side of the plate in the "overpasted" condition, especially if belt pasters are used.
In addition, many of the problems with conventional batteries can be traced to existing pasting technology, including: (a) stratification of acid due to the lack of circulation caused, in part, by having the flat surface of the battery plate in contact with the flat surface on one side of the separator; (b) gas bubbles entrapped between the battery plate and the flat side of the separator which decreases overall efficiency; (c) the use of costly ribbed separators (to partially alleviate acid stratification and gas bubble entrapment); (d) inefficient active material utilization resulting from the use of non-tapered plates with smooth surfaces, (i.e., utilization at the top of the plate is greater than that at the bottom); and (e) increased internal resistance resulting from the gap between the separator and the battery plate when ribbed separators are used.
The third aspect involves plate curing. Lead-acid battery plates are cured after pasting in order to oxidize any free lead in the plate, obtain the desired crystal structure of lead sulfate in the plate, convert the paste to a strong crack-free mass that can be easily handled, and improve adhesion to the grid. See U.S. Pat. Nos. 1,806,108; 4,342,342; and 4,499,929.
Curing is usually accomplished by (a) treating stacks of pasted plates prepared from cast grid "doubles" in curing chambers under conditions of controlled temperature and humidity or (b) "aging" stacks of plates under ambient conditions using moist burlap covers to help retard the rate of drying caused by the exothermic reaction which takes place. In the former instance total cure time is quite long, ranging from three to five days, and humidity is controlled by the injection of steam into the chamber. "Aging" requires even longer times and does not yield consistent curing conditions from batch to batch.
In spite of attempts to control and accelerate the process by using controlled curing chambers, plate quality normally varies because curing chambers are usually emptied and filled once per shift (i.e., once per eight hour period). Thus plates prepared earlier in the shift begin to cure at room temperature and can cure for as much as seven hours longer than plates prepared later in the shift. Also, the stacking of plates causes inconsistencies, as plates in the middle of the stack are subjected to different conditions of temperature and humidity than are those at either end.
In battery element manufacture, the fourth aspect, the combining of cured positive and negative plates and insulating separators into cell elements is normally accomplished by preparing a stack of alternating positive and negative plates having porous, insulating separator material located between each individual plate. See U.S. Pat. No. 4,539,273 and Japanese Patent No. 55-130076. The ampere-hour capacity and performance at high discharge rates of the cell element is normally controlled by the number, size, and thickness of the plates in the battery element. Because of the proliferation of battery sizes required in today's markets, a very large number of cell elements which differ in size, thickness, and number of plates, are required to manufacture the multitude of batteries of varying reserve capacity and cold cranking capability required to be manufactured in each battery plant. This, in turn, requires that the manufacturer produce and inventory plates of many different sizes along with a multitude of battery boxes capable of holding elements made up of various numbers of plates. These factors all greatly increase the cost of manufacture.
The cost of manufacture of cell elements and batteries produced therefrom is further increased by the relatively inefficient way in which cell elements are currently assembled and placed into the battery container. The most common method involves individually enveloping each positive plate (or in one instance, each negative plate) by folding a flexible porous separator material around the bottom of the plate and sealing, as by welding or mechanical locking for example, the vertical edges of the separator which overlap the edges of the plate. See U.S. Pat. No. 4,657,799. After this, the enveloped plates are stacked in alternating fashion with plates of opposite polarity until the desired number of positive and negative plates has been achieved. The plates are then aligned by vibrating the stack. After alignment the stack is inverted so that the plate lugs are "down", the stack is then lowered into molds containing molten lead which solidifies to form straps connecting all of the positive plates and all of the negative plates, respectively, thereby forming a finished element. Finally, the elements are placed into a battery box containing individual compartments which have been sized to take a particular element.
In battery manufacturing plants which handle most of the above operations mechanically, a large amount of manual labor is still required. In less sophisticated plants, the process is slow and very labor intensive, and control of product quality is difficult to achieve.
The fifth and final aspect involves containerization. It is known to use the battery container as a means of aligning and holding the cell elements as they move through the cast-on strap operation during which all positive plates in each cell and all negative plates in each cell, respectively, are joined together. See U.S. Pat. Nos. 3,753,783; 3,791,874; 3,915,751; 4,144,927; and 4,509,253. Similar problems as discussed hereinabove with respect to labor costs, manufacturing inefficiencies and raw material waste are also present in known conventional containerization processes.
As will be appreciated from the above, there remains a need for a better performing, lightweight and higher quality lead-acid battery. In addition, there also remains a need for a more efficient, economical, and automated method and associated apparatus for producing not only this improved battery but also other types of lead-acid batteries.